NOTES ON DESTRUCTION PERKS

The Impact perk is potentially extremely powerful and can be used to stunlock opponents. Even Apprentice level spells such as Firebolt can stagger powerful enemies.

That said, dual casting Destruction spells will eat through magicka extremely quickly. Casters who rely on Destruction as a primary source of damage should focus on obtaining items that reduce the cost of Destruction spells.

Items that increase Magicka regen are useful, but keep in mind there is a large penalty to magicka regen while in combat. In many cases items and perks that reduce spell cost and increase maximum magicka can be more effective.

The three 'spell effects' perks are a mixed bag. Intense Flames and Disintegrate can actually be detriments, as chasing down fleeing enemies is annoying and disintegrated corpses cannot be raised as zombies. Deep Freeze is decent but often only kicks in when you're winning the fight anyway.

Building Destruction

You've got the magic mainstays: fire and ice magic, along with lightning damage. These spells are incredibly powerful by themselves, but each have bonus effects, too.

Fire - Fire damage often applies an after-effect that damages the target over time from residual burns.

Ice - Targets that suffer from ice damage take hits to Stamina as well as Health.

Lightning - Targets hit with lightning magic get some of their Magicka reserved disintegrated as well. In addition, close impact from the spell usually instantly kills.

You can see these specific spells have uses beyond the direct, initial damage. Destruction Dual Casting is especially devastatingly powerful. It supercharges two single spells of the same type and morphs it into one powerful face-melter. When paired with Impact, the results are lights-out for the target.

SPELL MECHANICS AND SITUATIONAL USE

Fire projectile spells such as Firebolt, Fireball, and Incinerate travel at arrow-like speed but in a straight line away from the caster. This makes them ideal for use on distant, large, slow moving or stationary targets. Additionally, they set the target on fire(targets on fire take extra damage).

Ice spells often travel more slowly (excepting Icy Spear) but can be used to limit a target's mobility. They are excellent against melee attackers. However, a large number of Skyrim's human enemies are Nords and have innate frost resistance.

Lightning bolt spells have limited range compared to Fireballs, but arc nearly instantly from caster to target. This makes them ideal for targeting foes at mid-range including archers on ramparts or airborne dragons, and can even make hitting charging melee opponents a little easier. In addition, shock resistance is very rare compared to fire or frost (particularly with dragons, which are highly resistant to their breath element). All this makes Lightning an excellent all-around choice. Lightning is a good choice against mages and dragon prisests since it destroys the target's magicka as well.

Frost is your enemy

...especially if you're a melee-type character.

Frost spells aimed at you will almost always drain your Stamina as well as your Health; keep this in mind for when you are equipping your character, as that old amulet of 13% frost resist might still be a useful defense. Also, make sure to look for Perks that improve your resistance to spells, as there's nothing quite so frustrating as running in painfully slow-motion while a Forsworn mage is blasting ice at you, and all you can do is curse his stupid hat and down health and restore stamina potions like a binge drinker.